Abstract: Substantial increases in the human population along Florida’s east coast create a variety of anthropogenic stressors in adjacent coastal ecosystems. In particular, opportunistic pathogens related to degradation in water quality are of concern to both wildlife and public health. The objective of this study was to identify spatial, temporal, and environmental risk factors for E. coli colonization among Atlantic bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon (IRL), FL between 2003 and 2007. Age, gender, location of capture, coastal human population density, proximity of sewage treatment plants, total number of septic tanks, cumulative precipitation 48 hrs and 30 days prior to capture, salinity, and water temperature were analyzed as potential risk factors. Highest E. coli colonization rates occurred in the northern segments of the IRL. The risk of E. coli colonization was highest among the youngest individuals, in counties with the highest cumulative rainfall 48 hrs prior to capture, and in counties with the highest number of septic systems during the year of capture. The prevalence of colonization was highest during 2004, a year during which multiple hurricanes hit the coast of Florida potentially leading to increased runoff and bacterial loading of the IRL. The greater number of septic tanks in the northern segments in combination with weather-related events suggests a possible pathway for introduction of fecal coliforms into estuarine ecosystems. The ability of E. coli and related fecal coliform bacteria to act as primary pathogens or cause opportunistic infections adds to the public health importance of these findings from a sentinel species.